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1. Field of the Invention
This invention relates to wireless communication systems, such as those including automatic retransmission and error recovery for packet oriented point-to-multipoint communication.
2. Related Art
In communication systems, messages from a sender to a receiver using a communication link are sometimes subject to sending errors, such as bit errors, unreasonable sending delay, unintended reordering, and unintended duplication of messages. For example, noise on the communication link can cause bits within messages to be incorrect, generally causing the receiver to be unable to use the message. In a wireless communication system, these problems are exacerbated by a variety of circumstances that are specific to wireless communication. For example, co-channel interference (CCI), multipath and multipoint effects, such as refraction or reflection resulting in intrasymbol interference and intersymbol interference, are often prevalent with wireless communication, and can substantially reduce the reliability of wireless communication links.
One known method in digital communication systems is to implement an automatic retransmission protocol between sender and receiver, so that the receiver acknowledges messages from the sender, and the sender re-transmits those messages not acknowledged by the receiver within a reasonable time. Known automatic retransmission protocols include several parameters, which must generally be selected in response to characteristics of the communication link, to optimize communication throughput between the sender and receiver.
One problem with application of this known method to wireless communication systems is that there are multiple physical characteristics of the wireless communication link, each which is specific to a particular combination of sender and receiver, and each of which can change substantially over relatively short time durations. These multiple physical characteristics can include characteristics of the sender""s equipment or of the receiver""s equipment, characteristics of objects on or near communication pathways between the sender and the receiver, and characteristics of other communications overlapping communication between the sender and the receiver. For example, the wireless communication environment can include substantial changes in wireless communication link characteristics in the time duration between sending a message and sending an appropriate acknowledgement for that message. This is particularly so for characteristics related to errors in sending information using wireless communication links, including interference such as CCI, and multipath and multipoint effects. Moreover, multiple ones of these physical characteristics can change independently of one another, and can have substantial and relatively unpredictable effects on one another.
Accordingly, selection of a single set of parameters with which to optimize automatic retransmission using a wireless communication link is virtually always suboptimal for communication among multiple senders and multiple receivers. Moreover, selection of parameters with which to optimize automatic retransmission can be subject to substantial data collection and computation; this task is not easily distributed among multiple senders and multiple receivers. Accordingly, it would be advantageous to provide a technique for automatic retransmission and error recovery for packet oriented point to multipoint communication, that is not subject to drawbacks of the known art. Preferably, in such a technique, automatic retransmission and error recovery characteristics are responsive to changes in the characteristics of the communication link between sender and receiver.
The invention provides a method and system for point to multipoint wireless communication, including automatic retransmission and error recovery for packet oriented point to multipoint communication. The method and system integrates adaptive and dynamic responsiveness for parameters for automatic retransmission using wireless communication, both for single sender and a single receiver, and for sets of multiple senders and multiple receivers. In a first aspect of the invention, the wireless communication link is divided into a downstream portion and an upstream portion. The method and system selects parameters for automatic retransmission independently for the downstream portion and the upstream portion of the wireless communication link. A base station controller (BSC) controls the selection of parameters for automatic retransmission for all customer premises equipment (CPE) within a cell. As part of a TDD frame, in which the BSC and the CPE share communication bandwidth using a TDMA technique, the BSC includes its selection of parameters for automatic retransmission to be used by CPE within a control section of the TDD frame.
Preferably in this aspect of the invention, the BSC dynamically and adaptively determines new selected parameters for automatic retransmission, in response to conditions of a wireless communication link with each independent CPE. One problem particular to this aspect of the invention, and overcome by the invention, is that when the BSC sends new selected parameters for using the wireless communication link, aspects of each message to be sent will also dynamically vary. These can include the size of each message (in bytes or message symbols), the time duration for each message, and other aspects of each message. Accordingly, in the second aspect of the invention, parameters for automatic retransmission are responsive to a number of bytes successfully sent from a sender to a receiver, rather than responsive to a number of messages successfully sent or a number of symbols successfully sent.
In a second aspect of the invention, upstream retransmission control is placed in the receiver of the upstream communication (i.e., the BSC) rather than the transmitter of the upstream communication (i.e., the CPE). In order to control retransmission, the BSC dynamically and adaptively allocates acknowledgement time slots within the upstream portion of the TDD frame for use by each selected CPE. Thus, the BSC, in addition to determining parameters for automatic retransmission, also determines an amount of bandwidth allocated to each selected CPE for sending messages associated with automatic retransmission (such as acknowledgement or non-acknowledgement messages). As part of this second aspect of the invention, the BSC allocates some portion of the upstream bandwidth as a shared resource and some portion of the upstream bandwidth as unshared (that is, specifically allocated to a selected CPE) when there are messages received but not yet acknowledged.
In a third aspect of the invention, the BSC dynamically and adaptively responds to acknowledgement and non-acknowledgement messages from each selected CPE, to integrate the automatic retransmission protocol with the TDD frame and the TDMA technique used within that frame. In a preferred embodiment, when the BSC sends messages to a selected CPE, the BSC sets a first timeout each time it receives a non-acknowledgement message from that selected CPE; during this first timeout duration, the BSC discards further acknowledgement and non-acknowledgement messages from that selected CPE. Also in a preferred embodiment, when the BSC receives messages from a selected CPE, the BSC sets a second timeout each time it receives an invalid message from the selected CPE; during this second timeout duration, the BSC discards all further messages received from that selected CPE.
The invention provides an enabling technology for a wide variety of applications for communication, so as to obtain substantial advantages and capabilities that are novel and non-obvious in view of the known art. Examples described below primarily relate to wireless communication systems, but the invention is broadly applicable to many different types of communication in which characteristics of the communication link are subject to change.